1. Field of the Invention
The present invention relates to a coordinates input apparatus of an optical detection type which is attached on a front surface of a display unit for detecting a position of coordinates in a display surface thereof and for inputting the position of coordinates to a computer, and in particular, to a countermeasure for preventing dust.
2. Description of the Prior Art
Coordinates input apparatuses for manually inputting data of positions of coordinates to a computer are constructed in various types, for example, electromagnetic induction, electrostatic capacitance, transparent electrode, and optical detection types. Among these various types of coordinates input apparatuses, the optical detection type has attracted attention with respect to reliability and operability in which the apparatus is mounted on the front surface of a display unit and when an arbitrary position on the display surface of the display unit is pressed by a finger or the like to interrupt a path of light, the location of coordinates can be defined without directly touching a device detecting the coordinates position. (This type of apparatus is simply referred to as a coordinates input apparatus 12 herebelow).
FIGS. 12-16 are diagrams illustrating the prior art coordinates input apparatus. FIG. 12 is a perspective view of the coordinates input apparatus mounted on the front surface of a display unit. FIG. 13 is a cross-sectional view illustrating the main portion on a light receiving side of the coordinates input apparatus. FIG. 14 is a schematic diagram of the rear side illustrating an internal structure of the coordinates input apparatus with the rear panel removed.
In these diagrams, the coordinates input apparatus primarily comprises a frame 1 in a form of approximately a rectangle having an opening section 2 at a central portion thereof, pairs of a plurality of light emitting elements 4 such as LED's and a plurality of light receiving elements 5 such as phototransistors, the light emitting elements 4 and the light receiving elements 5 being disposed on the opposing edges, respectively on the rear side of the frame 1, namely, on the side opposite to a display surface 3a of a display unit 3 using a CRT or the like, and an arithmetic/operation unit 6 for detecting from the pairs of the light emitting elements 4 and the light receiving elements 5 a position where a light path 10 is interrupted and for inputting the position.
The light emitting elements 4 and the light receiving elements 5 are fixedly mounted on a base plate 7 disposed in the frame 1 in such a fashion that a light emitting section 4a and a light receiving section 5a of each pair of the elements 4 and 5 oppose to each other; whereas on the front surface of a light receiving section 5a of the light receiving element 5, a light blocking plate 8 having light passing holes 8a with a predetermined area is so disposed that only an incident light from a light emitting element 4 paired with the light receiving element 5 can be received. Moreover, on the front side of the light blocking plate 8 and the light emitting elements 4, namely, in the peripheral portion of an operation area A, an infrared-ray filter 9 is mounted on the overall regions thereof to block the visual light. Consequently, an invisible light path 10 is formed by use of the ultrared-ray filter 9 in the operation area A on the front side of the display surface 3a.
Next, a description will be given of the principle of an input operation of the coordinates input apparatus having above-mentioned configuration. For example, as shown in FIG. 12, if a finger 20 or the like touches a location on the display surface 3a to input the coordinates data thereof, the light path 10 associated with the location is blocked, which enables to define the position of the coordinates. That is, by sequentially causing light emission of the light emitting elements 4 to effect scanning, the blocked light path 10 in the x and y directions can be detected by use of the light receiving elements 5. The light path 10 is determined by the arithmetic/operation unit 6 and the position of the coordinates is transmitted to the host computer (not shown).
As another prior art example, FIGS. 15-16 show an apparatus having a Video Display Terminal (VDT) filter disposed on the front side of a CRT display. FIG. 15 is a cross-sectional view of the primary section on the light receiving side, whereas FIG. 16 is a rear view illustrating the inner configuration thereof with the rear panel removed.
The coordinates input apparatus primarily comprises a frame 1 in a form of approximately a rectangle having an opening section 2 at a central portion thereof, pairs of a plurality of light emitting elements 4 such as LED's and a plurality of light receiving elements 5 such as phototransistors, the light emitting elements 4 and the light receiving elements 5 being disposed on the opposing edges, respectively on the rear side of the frame 1, namely, on the side opposite to a display surface 3a of a display unit 3 using a CRT or the like, and an arithmetic/operation unit 6 for detecting from the pairs of the light emitting elements 4 and the light receiving elements 5 a position where a light path 10 is interrupted and for inputting the position of the coordinates to the host computer. Each terminal of the light emitting elements 4 and the light receiving elements 5 is soldered on a base plate 7 disposed in the frame 1 in such a fashion that a light emitting section 4a and a light receiving section 5a of each pair of the optical semiconductor elements 4 and 5 oppose to each other.
At the opening section 2, there is provided an operation panel 11 comprising a VDT filter to enhance the visibleness of the display surface 3a of the display unit 3 and to prevent dust from being attached to the display surface 3a. A light blocking plate 8 having light passing holes 8a with a predetermined area and a predetermined depth is disposed on the front side of the light receiving elements 5 arranged in a column form so that only an incident light from the associated light emitting element 4 is received. Moreover, on the front side of the light blocking plate 8 and the light emitting elements 4, an infrared-ray filter 9 in a form of a rectangular frame is disposed in the entire periphery to block the visible light. Namely, the front side of the light receiving elements 5 arranged in a form similar to L and the front side of the light emitting elements 4 arranged also in a form similar to L oppose to the respective outer surfaces of the infrared-ray filter 9 in an rectangular form; and an end section 9a of the filter 9 opposes to the periphery of the operation panel 11. Consequently, on the front side of the operation panel 11, namely, on a side not opposing to the display surface 3a, an invisible light path 10 is formed by use of the infraredray filter 9.
For example, when a position of the operation panel 11 associated with an input position of the display surface 3a is pressed by a finger 12 to input the data of the position as shown in FIGS. 3 and 5, a light path 10 passing through the pressed position 20 is blocked among the light paths formed along the surface of the operation panel 11. Consequently, by sequentially effecting light emission of the light emitting elements 4 to perform the scanning, the blocked light path 11 in the x and y directions can be detected by use of the light receiving elements 5. The blocked light path 10 is determined by the arithmetic/operation unit 6 and the position of the coordinates is outputted to the host computer (not shown).
Such a conventional coordinates input apparatus is accompanied by a problem that dust in the air and dust fixed on the display surface 3a due to static electricity are drawn by an air flow indicated by an arrow mark in FIG. 13 to enter a space B between the infrared-ray filter 9 and the light receiving elements 5, namely, dust is likely to fix on the inner surface of the infrared-ray filter 9 and on the light receiving section 5a of the light receiving elements 5. This is also the case on the side of the light emitting elements 4, that is, dust is likely to attach on the light emitting section 4a. When dust fixes on the inner surface of the infrared-ray filter 9 and on the light receiving section 5a, the light transmittivity is considerably lowered, which may lead to a malfunction. Moreover, to prevent such a malfunction, the cleaning operation must be frequently conducted to remove the dust and the maintenance becomes complicated accordingly. Especially, an air flow is forcibly generated along the direction of the arrow mark as shown in FIG. 13 when a cooling fan is included in the display unit 3, which causes a considerable amount of dust to be fixed on the inner surface of the infrared-ray filter, the light emitting section 4a, the light receiving section 5a, and the like.
In the prior art coordinates input apparatuses the infrared-ray filter 9 formed with acryl resin or the like must be engaged with or fixed to the frame 1 formed with ABS resin or the like as shown in FIG. 13. Since the junction therebetween is exposed on the operation area A, the junction must be carefully conducted not to deteriorate the design of the apparatus, namely, stepped portions must not be formed and excessive adhesives must not be remained, which leads to a problem that the assembling operation becomes complex. Moreover, in such a conventional coordinates input apparatus, if an infrared-ray filter 9 formed with a hard material is designed to be tightly fixed to the operation panel 11 and the display surface 3a, there arises a danger that the filter 9 is damaged because of a dimensional error or the like; and hence a slight space 13 is disposed between the end section 9a of the filter 9 and the opposing section thereof, namely, the peripheral sections of the operation panel 11 and the display surface 3a. As a result, the dust in the air or the dust fixed on the operation panel 11 or the display surface 3a due to static electricity are drawn by the air flow into the space A (FIG. 15) on the rear side of the infrared-ray filter 9. The dust is then fixed on the rear surface of the infrared-ray filter 9, the light emitting section 4a, the light receiving section 5a, and the like, and hence the light transimittivity is likely to be reduced and a malfunction is caused. As a further problem, the cleaning operation must be frequently conducted to remove the dust and thus the maintenance becomes complicated.
The conventional optical coordinates input apparatus as described above cannot be adopted, particularly, as an apparatus to be borne on a vehicle.